In the commercial and defense industries, users are demanding technology integration that increases product life, simplifies operation and maintenance, and provides integration that improves safety and reliability. However, any technology offered must also support a positive, quantitative cost/benefit analysis.
Fiber optic sensors have been used for the measurement of relative position for decades, but, until the present invention, their utility has not been extended to self-calibrating, precision absolute, position measurement systems. While conventional systems using fiber optic sensors offer only a relative measurement capability, they usually require repetitive calibration between uses because they are sensitive to the angle of the surface being measured and the distance between the sensor and the surface being measured. Indeed, some of those skilled in the art may believe that precision absolute position measurement systems could not be accomplished with fiber optic sensors.
Most sensor prognostic systems require exorbitant amounts of processing power for determining statistical probabilities or require precise measurements of physical properties for which current sensor technology does not exist. For example, in prognostic measurements of a moveable shaft (such as may be found in an aircraft engine or similar vehicle engine), the operational characteristics of the shaft must be known to ensure safe aircraft operation. Some operational characteristics required include monitoring of shaft lateral displacement, shaft misalignment, shaft speed and torque, all characteristics, which are difficult or impossible to capture with current non-contact sensor technology. These characteristics may be necessary to determine in such applications as turbogenerators, power generation stations, ships, submarines and earth moving equipment.
The need to measure drive shaft alignment has existed for some time. In flexible or fairly rigid structures, a moveable shaft (for example, one that is rotating) can move out of alignment, bend beyond its stress points or move off a set axis, thereby resulting in a damaged structure, engine or system. For example, aircraft safety depends in part on determining the drive's operational characteristics as torque is transmitted to any engine component. Further, the shaft's attitude and bending characteristics needs to be non-invasively measured, as well as the shaft's rotational speed and torque. Movement, either from the shaft attitude or the bending, needs to be measured to less than 0.01 inches (i.e., 10 mils) and the RPM and the torque further needs to be monitored.
Two known previous technical approaches to measuring and monitoring the shaft have been unsuccessful. For example, Lucent Technologies attempted to use an eddy-current sensor; however, measurements based on eddy-current sensing did not provide the accuracy, environmental tolerance, or robustness required for this or similar applications. Others have attempted a design concept that required a magnetic slug embedded in the torque couplers. However, this method similarly proved unsuccessful.
Thus, there is a need for a non-obtrusive system that optically measures movement of a large drive shaft or torque coupler in the confined space of an engine such as, for example, an aircraft. The sensor system must not interfere with airflow into the engine, and must accommodate various environmental conditions (such as, for example, high vibration, shock and high temperature conditions). Preferably, the sensor must also be placed between 150 mils and 500 mils from a surface of the face of the drive shaft or coupler assembly due to space constraints. The sensor system must also be capable of capturing absolute measurement of the shaft's movement without calibration. Moreover, the measurement data obtained by the sensor system should be capable of determining movement of 10 mils or less in the application as the shaft rotates up to 9000 revolutions per minute (RPM). The system should also preferably measure rotation of the shaft at greater than 9000 RPM as well as twisting of the moveable shaft in order to calculate torque. The system should also be able to measure absolute distance from each sensor to a surface on the torque coupler knowing that the surface may vary not only in axial distance away from the sensors but also in complex angles relative to the sensors. The ability to non-obtrusively measure absolute movement versus relative movement, high-resolution shaft displacement, and twisting in the moving shaft has never been accomplished before the present invention.
A self-calibrating, precision absolute position measuring system, such as disclosed in the present invention, is also supported by the defense community. The Secretaries of the Army, Navy, and Air Force have all directed, by policy, that new procurements must incorporate diagnostic and prognostic system health management prior to funding approval. This has been emphasized in new development programs including the Crusader for the Army, the Advanced Amphibious Attack Vehicle for the Marines, and the Joint Strike Fighter (JSF) for the joint services. However, until the present disclosure, there was a gap between the need and the technology available to meet that need.